What hose should I choose for a sump pump?
Choose a hose at least as wide as the pump outlet, as short as possible and without kinks. For a 1 1/4-inch outlet, this means 32 mm. A flat hose is sufficient for occasional use. For a permanent installation, choose reinforced spiral hose or rigid PVC, with stainless steel clamps.
32 to 38 mmcommon diameter for a 1 1/4 to 1 1/2-inch outlet
2 mof hose to add to the calculation for each elbow
More than 3 mof hose: KSB recommends a dirty water check valve
Diameter: never smaller than the outlet
The manufacturer KSB gives a simple rule: the discharge diameter must be at least equal to that of the pump outlet. In our shop, sump pump outlets are often 1 1/4 or 1 1/2 inches. Kärcher summarizes the other half of the rule: the shorter and wider the hose, the higher the flow rate.
Narrowing the hose quickly costs you, as the water rubs more in a small hose. The diagram shows KSB's table for 10 m of hose.
Check the inner diameter, because that is what matters and must fit over the fitting. Many pumps come with a stepped nozzle, for example 32/25 mm. If your hose is 32 mm, remove the 25 mm part: leaving it in place would create a bottleneck.
What type of hose to use depending on the application
Flat hose: for occasional use
Flexible and compact, it unrolls quickly and takes up little space. It is suitable for a flooded basement or occasional emptying. Its weakness: it crushes and kinks easily, which slows down the water. Unroll it completely before starting.
Reinforced spiral hose: the right compromise
It keeps its shape in corners and does not kink as easily. Our reinforced PVC hoses of 32 and 38 mm operate at 6 bar, are frost-resistant, can be used for both suction and discharge, and can be buried.
Rigid PVC: for permanent installation
For a permanently equipped pit, it offers a clear path along the wall. Allow for wide elbows and mounting clamps, and limit their number.
Garden hose: for emergency use only
It is too narrow to empty quickly. Kärcher even recommends a pre-filter below 1 1/4 inch, to prevent the pump from clogging.
Length and height: the calculation to make
The pump must overcome two things: the height to overcome and the friction in the hose. Count each elbow as 2 m of additional hose, as KSB and Michaud-Chailly do.
Example: 2.5 m of height, 10 m of hose and 2 elbows, at 6 m³/h. This makes 14 m of calculated length.
- In 32 mm: 1.9 m of losses, or about 4.4 m in total.
- In 40 mm: 0.9 m of losses, or about 3.4 m in total.
Then look for this height on your pump curve. The maximum height of the sheet corresponds to almost zero flow: you need to read the available flow at your actual height. Our article on choosing a sump pump details these criteria.
Before cutting, unroll the hose over the actual path. One meter less and one avoided elbow are often better than a more powerful pump.
Connecting without leaks or water return
- Clamp: tighten a stainless steel clamp on the nozzle. Gardena recommends an additional clamp for 38 and 50 mm hoses.
- Check valve: KSB recommends a non-return valve for dirty water and hoses longer than 3 m. Some models include one, such as the DAB Nova UP. Otherwise, a 1 1/2-inch spring check valve can be installed with the appropriate threaded fittings.
- Path: remove any kinks and secure the hose so it does not move when the pump starts.
- Winter: an outdoor hose must remain empty if your model is sensitive to frost. The pump is stored indoors.
Do not run a pump dry: Kärcher and Gardena remind that this wears it out. Do not leave the discharge closed either: Gardena sets the limit at 10 minutes on its models. Before starting, check that the hose is neither kinked nor clogged.
Useful product references
Hoses are sold by the meter. For occasional use, the Oase kit combines the pump and a 10 m hose.
32 mm flexible PVC hoseReinforced, 6 bar, frost-resistant, sold by the meter. For 1 1/4-inch outlets.View product38 mm flexible PVC hose38 mm inner diameter, reinforced, 6 bar. For 1 1/2-inch outlets or long runs.View productStainless steel hose clamp304 stainless steel, worm gear tightening, from 9 to 80 mm.View productProMax ClearDrain 6000 KitSump pump and 10 m flexible hose. G 1 1/4 connection, elbow and stepped nozzle included.View product
Unsure about the diameter or length? Send us the pump model, the height and the distance.
Ask my questionFrequently asked questions
What diameter for a 1 1/4-inch pump outlet?
Take at least the outlet diameter, which means 32 mm in practice. If the distance is long or the flow rate is high, a larger hose loses less height, provided you use the right fittings.
Can a garden hose be used on a sump pump?
For a small flow rate or the end of flat pumping, some pumps accept it with the right fitting. To empty quickly, it is too narrow. With a hose smaller than 1 1/4 inch, Kärcher also recommends a pre-filter to prevent clogging.
Flat hose or spiral hose: which one to choose?
The flat hose is suitable for occasional use, as it rolls up easily. The reinforced spiral hose is better suited for a permanent installation or a path with corners, as it does not crush.
What is the maximum hose length?
There is no single limit. Add the height to overcome and the head losses, then check the remaining flow at this height on the pump curve.
Is a non-return valve needed?
KSB recommends it for dirty water and hoses longer than 3 m. Check your pump first: some models, such as the DAB Nova UP, have one built-in.
Read also
For fittings: The advantages of using flexible fittings for your pond and filter
READ THE ARTICLE
Read also
For the check valve: Where to place a non-return valve on a pond: pump, filter, suction and air pump
READ THE ARTICLESources and references
Last updated: November 4, 2026.
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